The present invention is concerned with self-curing concrete and in particular to internal curing compositions and methods of using said compositions for curing concrete.
Curing compositions are well known in the concrete art. They are materials which are applied to the surface of wet concrete to reduce or eliminate the loss of water from the concrete and therefore result in a better concrete which has lower permeability and therefore better strength and durability. These are typically emulsions of paraffins or microwaxes which are sprayed on to the surface. While these serve the purpose well, it is not always desirable to leave them on the surface to wear away by exposure to the elements, and removal can be costly and time-consuming.
It has been suggested that concrete can be cured by an xe2x80x9cinternalxe2x80x9d curing admixture, that is, by the addition to and mixing into a concrete mix of an admixture which provides curing. While such compositions have been used in specialised applications such as shotcrete application, to date no such composition has been found to be able to meet the standards required in general concrete applications, for example, Australian Standard AS 3799.
The object of the present invention is to ameliorate at least some of the disadvantages of the prior art or to provide a useful alternative.
The present invention is based on the observation that a combination of a wax and a glycol, when added to concrete, enables internal curing of concrete which in many respects is equal to or superior to traditional forms of curing concrete, as assessed by a number of relevant parameters. The present invention provides for the first time an internal curing composition which, when added to concrete or other cementitious mixes, meets the required standards of curing (Australian Standard AS 3799).
According to a first aspect there is provided an internal curing composition including a glycol and a wax.
The preferred glycols are polyethylene glycol (PEG) and methoxypolyethylene glycol (MPEG). The PEGs have weight-average molecular weights (MWs) of from 200 to 10,000 and the MPEGs have MWs of from 350 to 5,000. The most preferred materials are PEGs with MWs of about 200.
The waxes for use in this invention are preferably selected from paraffin wax, microcrystalline wax and mixtures thereof, the preferred wax being paraffin wax.
A preferred internal curing composition according to the invention includes a paraffin wax and a PEG of MW about 200.
The preferred ratio of glycol to wax is from about 1:3 to about 1:12. More preferred is a ratio of about 1:4 to about 1:8. Even more preferred is a ratio of about 1:6.
According to a second aspect there is provided an internal curing concentrate including a composition according to the first aspect and water.
Preferably the concentrate includes from about 5% to about 15% polyethylene glycol, from about 52% to about 62% paraffin wax and from about 23% to about 43% water. Even more preferred is a concentrate which includes about 10% polyethylene glycol, about 57% paraffin wax and about 33% water. Also preferred is a concentrate with a high solids content, for example in excess of 50%.
Conveniently the concentrate is prepared in two parts, one including the paraffin wax and water, and the other polyethylene glycol. It would be understood however that polyethylene glycol and water may constitute one of the parts of the concentrate while the other part may be the paraffin wax. The two parts are combined to form the internal curing composition before addition to cement or a cementitious mix such as concrete. Optionally, the two parts of the concentrate may be added as separate components either simultaneously or sequentially in any order.
According to a third aspect there is provided a cementitious mix including a composition according to the first aspect or a concentrate according to the second aspect.
According to a fourth aspect there is provided a concrete mix including a composition according to the first aspect or a concentrate according to the second aspect.
Preferably the internal curing concentrate is present in an amount of about 2 I/m3 to about 10 I/m3 of cement or cementitious mix. Even more preferred is an amount of 5 I/m3.
According to a fifth aspect there is provided a method of preparing internally curing cementitious mix or internally curing concrete mix including combining cement and aggregate with a composition according to the first aspect or a concentrate according to the second aspect, in the amount sufficient to enable a slurry or a paste prepared from said cementitious mix or said concrete mix to cure.
According to a sixth aspect there is provided a method of preparing internally curing concrete structure including combining cement and aggregate with a composition according to the first aspect or a concentrate according to the second aspect in the amount sufficient to enable said concrete structure to cure.
Preferably the glycol and the wax are added simultaneously. It will be understood that, in alternative embodiments of the present invention, the glycol and the wax can be added sequentially in any order. Further, in preferred embodiments the internal curing concentrate is to be added without dilution. Optionally, however, the internal curing concentrate may be diluted with water before use.
According to a seventh aspect there is provided a method of preparing internally curing concrete structure including combining a mix according to the third or the fourth aspect and water.
According to an eighth aspect there is provided a cementitious mix, a concrete mix or a concrete structure, when prepared by the method of any one of fifth, sixth or seventh aspects.
The term xe2x80x9ccementitious mixxe2x80x9d as used in the context of the present invention is intended to include mixes such as mortar, concrete and such like, and which may include other additives such as lime, plasticizers, defoamers, retarders, accelerators, water reducers, etc. However, the term xe2x80x9cconcretexe2x80x9d may be independently used in reference to a mix of cement and aggregate consisting of sand and/or gravel, which may also contain lime and plasticizers, defoamers, retarders, accelerators, water reducers, etc.
The term xe2x80x9caggregatexe2x80x9d as used in the context of the present invention includes materials such as sand, gravel and the like.